1. Field of the Invention
This invention relates to the processing of semi-conductor wafers in a vacuum deposition apparatus. More particularly, this invention relates to an improved cleaning process for the removal of deposits, such as tungsten or tungsten silicide deposits, from a vacuum deposition apparatus without leaving fluorine residues.
2. Description of the Related Art
In the processing of a semiconductor wafer to form integrated circuit structures therein, it is desirable to deposit materials such as, for example, tungsten on the wafer by a chemical vapor deposition (CVD) process, either by a blanket deposition followed by a patterning step, or by selective deposition of tungsten over a mask layer, such as an oxide layer, already patterned to expose silicon or aluminum surfaces on which the tungsten will selectively deposit.
In either case, deposits of materials such as tungsten usually accumulate on the susceptor (base or support on which the semiconductor wafer rests during the deposition) in the CVD deposition chamber and such deposits must be removed periodically since they tend to change the dimensions of the chamber as well as to flake off the susceptor surfaces and onto the wafer being processed in the chamber, or change the deposition environment chemically, especially for subsequent selective deposition processes.
In the prior art, it has been conventional to remove such deposits using a plasma-assisted fluorine etch. A gaseous source of fluorine is fed into the vacuum deposition chamber and a plasma is then ignited in the chamber during the gas flow, by connecting to an rf source the faceplate through which gases are fed into the vacuum deposition chamber during the deposition. The base or susceptor on which the wafer normally rests during the CVD deposition will be grounded. The resulting fluorine chemistry reacts with the deposits, such as tungsten or tungsten silicide deposits, and the resulting reaction product is removed from the chamber by the vacuum evacuation system.
While this process satisfactorily removes tungsten or other deposits from the susceptor in the vacuum chamber, the cleaning process, in turn, leaves fluorine residues in the vacuum chamber which can interfere, for example, with subsequent tungsten depositions therein. If such a subsequent tungsten deposition in the chamber is a blanket deposition, the resulting tungsten layer will be non-uniform in thickness, probably due to inhibition of the tungsten deposition by the fluorine residues. If the next deposition is a selective tungsten deposition, the presence of fluorine residues in the chamber inhibits the deposition of tungsten on the exposed silicon or aluminum surfaces.
It would, therefore, be desirable to provide an improved process for the removal of deposits, such as tungsten and tungsten silicide deposits, from the susceptor in a vacuum chamber after a deposition such as a CVD tungsten depositions wherein no fluorine residues would remain in the deposition chamber at the conclusion of the cleaning process.